For coloring an aromatic polymers, such as polystyrene, styrene/acrylonitrile copolymer (AS) and styrene/acrylonitrile/butadiene copolymer (ABS), there have been employed principally dry coloring, color compounding and masterbatch preparation. All these techniques employ a dispersant for dispersing the pigments uniformly over the polymer mass.
Japanese Patent Kokai Sho 58-103530 A discloses a dispersant for pigments for polymers based on styrene, which comprises a grafted polyolefin wax obtained by grafting a styrene-based compound onto a polyolefin wax. While this pigment dispersant excels in the performances for dispersing pigments and the like, it requires two process steps of polyolefin synthesis and grafting of styrene-based compound thereon, resulting in higher production cost. There is also a demand for a more superior pigment dispersing ability.